Showing papers on "Tungstate published in 1997"
TL;DR: In this paper, the acid activity of the solid tungsten/zirconia can be affected by the catalyst preparation method, and it is shown that refluxing of the hydrous zirconias prior to tengsten impregnation gives a catalyst with higher surface area than the nonrefluxed material, but with the same strong acid site density, as determined by n -pentane isomerization activity.
192 citations
TL;DR: In this paper, the effects of the content, which is related to the age of the deposition solution, and of mass transport on the deposition current and deposition efficiency were determined and used to elucidate the mechanism of electrodeposition.
Abstract: Electrodeposition of amorphous electrochromic tungsten trioxide was studied. Good quality films were deposited cathodically onto tin‐doped indium oxide (ITO) from a water/isopropanol solution containing dissolved tungsten(VI) species. Three reducible species are present in this solution: unbound , polytungstate ions, and peroxy‐tungstate ions. The effects of the content, which is related to the age of the deposition solution, and of mass transport on the deposition current and deposition efficiency were determined and used to elucidate the mechanism of electrodeposition. Reduction of unbound and polytungstate did not result in film growth. This part of the current was under mixed diffusion‐kinetic control. The remainder of the current was due to reduction of peroxy‐tungstate and was kinetically limited. This process led to deposition. The current efficiency, defined as the number of electrons consumed by reduction of peroxy‐tungstate per W atom deposited, was about 1.6, in good agreement with the proposed deposition reaction.
161 citations
TL;DR: In this article, the effects of preparation parameters on the physical and chemical properties of zirconia-tungstate aerogels were studied and the catalytic activity and surface acidity were characterized by a set of chemical probes, including n -butane isomerization and pyridine adsorption.
118 citations
TL;DR: Ionic conduction of trivalent aluminum in solid aluminum tungstate, Al2(WO4)3, has been directly and quantitatively demonstrated in this paper by means of electrolysis and electromotive force measurement by constructing an aluminum concentration cell.
Abstract: Ionic conduction of trivalent aluminum in solid aluminum tungstate, Al2(WO4)3, has been directly and quantitatively demonstrated. Trivalent ions, especially for aluminum where the polarizability is considerably low, are strongly bonded in a crystal lattice and have been believed to be unlikely to exhibit migration in solids because of high electrostatic interaction with the surrounding skeleton structure. The material, Al2(WO4)3, which has the Sc2(WO4)3 structure, was selected in order to reduce the interaction between the framework and the mobile species, Al3+, as much as possible. The ionic conduction characteristics of Al2(WO4)3 were investigated by means of electrolysis and electromotive force measurement by constructing an aluminum concentration cell. The typical electrical conductivity of Al2(WO4)3 was, approximately 2 × 10-5 S cm-1 at 800 °C. The dc electrolysis data strongly support the conclusion that ionic Al3+ is the mobile species in Al2(WO4)3. By further electrochemical measurements, it was c...
90 citations
TL;DR: Carburisation of some compounds of nickel, tungsten and molybdenum produces powders which show considerable passivity in sulphuric acid at elevated temperature, and also show some catalytic activity towards the electro-oxidation of methanol and of hydrogen as discussed by the authors.
82 citations
TL;DR: In this article, metal tungstates containing Ni, Co, Zn, Fe, and Ce were investigated for paraffin oxydehydrogenation of propane, and it was found that the tungstate, in particular COWO{sub 4}, constitute a new class of catalysts holding some promise for parafin oxydeprogenation, in addition to the previously studied systems based on vanadium-containing compounds (1) and on nickel-cobalt-molybdates.
65 citations
TL;DR: In this paper, Raman, DRIFT, and 31P-MAS-NMR spectroscopies as pyrophosphates, chelate-bonded orthophosphate, and oligophosphates were characterized by adsorbed phosphate species.
Abstract: Phosphate-modified zirconia was prepared by impregnation of Zr(OH)4 and of m-ZrO2 with an aqueous solution of (NH4)2HPO4. Similar to sulfate and tungstate, phosphate shows a strong stabilizing effect on the specific surface area and the tetragonal phase of zirconia when using Zr(OH)4 as the precursor material. The adsorbed phosphate species were characterized by Raman, DRIFT, and 31P-MAS-NMR spectroscopies as pyrophosphates, chelate-bonded orthophosphates, and oligophosphates. Only a distortion of the geometry of the adsorbed phosphate species was found after dehydration of the materials in contrast to ZrO2/SO4. FT-IR spectroscopy with CO as a probe molecule was used to characterize the acidic properties of ZrO2/PO4. New hydroxyl groups, probably P−OH groups with enhanced protonic acidity as compared to pure zirconia but lower than that of ZrO2/SO4, were observed. In addition basic Zr−OH groups were observed. Furthermore, strong Lewis acidic centers (cus Zr4+), comparable to ZrO2/SO4, are formed by phosph...
57 citations
TL;DR: In this article, a novel displacement reaction process was used to combine reduction and carburization of ammonium tungstate or tungsten oxide in a single operation, resulting in an ultrafine grain size.
53 citations
TL;DR: In this paper, a polycrystalline film of BaWO4 was synthesized on tungsten metal substrates by hydrothermal-electrochemical and electrochemical methods from room temperature to 200 °C.
Abstract: Highly crystallized polycrystalline films of BaWO4 have been synthesized on tungsten metal substrates by hydrothermal-electrochemical and electrochemical methods from room temperature to 200 °C. The hydrothermal method did not produce a film because only discrete BaWO4 particles appeared on the tungsten substrate. The crystallization of BaWO4 was characterized by three-dimensional nucleation and growth behaviors. In the case of the electrochemical method, an amorphous tungsten oxide film formed after the BaWO4 film formation, while the hydrothermal-electrochemical method did not produce an amorphous film.
36 citations
TL;DR: In this paper, the aqueous chemistry of tungsten offers several possibilities for the synthesis of homogenous molecular precursors containing W and Co mixed on the atomic scale.
31 citations
TL;DR: A cell-free preparation from avocado fruit incorporates [14C]mevalonate into ABA and the potential for using the tungstate/cinchonine reaction to probe other biosynthetic pathways which require a molybdate ion is discussed.
Abstract: A cell-free preparation from avocado fruit incorporates [14C]mevalonate into ABA. A number of specific inhibitors have been used to probe the system and tungstate ions at 100 µM reduce the 14C in ABA by 80% The inhibitory effect was overcome by the alkaloid cinchonine (2000 µM) which binds tungstate strongly and selectively. More 14C from mevalonate was present in xanthoxal (4600 dpm), less in ABA (340 dpm) when the cell-free system was inhibited by tungstate (100 µM) than in controls (1810 dpm in xanthoxal, 1200 dpm in ABA), which shows that xanthoxal is the substrate for the aldehyde oxidase. Xanthoxic acid, therefore, is the next intermediate and AB-aldehyde is not a normal precursor. The potential for using the tungstate/cinchonine reaction to probe other biosynthetic pathways which require a molybdate ion is discussed.
TL;DR: Three new compounds, AgLnW, GdW and Tb, have been prepared by a solid-state reaction and crystallize with a scheelite-related monoclinic symmetry.
Abstract: Three new compounds, AgLnW
2
O
8
(Ln
3+
=Eu, Gd or Tb), have been prepared by a solid-state
reaction and crystallize with a scheelite-related monoclinic symmetry.
Their IR spectra show absorption transitions in the region 1000–400
cm
-1
similar to KLnW
2
O
8
. Broad
excitation and emission bands of the tungstate group with a large Stokes
shift (12 573 cm
-1
) are observed in
AgGdW
2
O
8
. Excitation and emission spectra of
AgLnW
2
O
8
(Ln=Eu or Tb) show that energy transfer
from tungstate to Eu and Tb occurs and that Eu
3+
ions occupy a
unique crystallographic site with C
2
site
symmetry.
TL;DR: The polyoxometallate Keggin (αtype) [PMo4.27W7.73O6−40] [H3N(CH2)6NH2+3]3, involving molybdenum and tungsten present in both V and VI oxidation states, has been synthesized under hydrothermal conditions and its structure determined by single crystal X-ray analysis.
Patent•
30 Jun 1997
TL;DR: In this article, a catalyst for the synthesis of methyl mercaptan from hydrogen sulfide and methanol is described, which contains active aluminum oxide on which 15% to 40% by weight cesium tungstate is deposited as the activator.
Abstract: A catalyst for the synthesis of methyl mercaptan from hydrogen sulfide and methanol, as well as a process for preparing the catalyst. The catalyst contains active aluminum oxide on which 15% to 40% by weight cesium tungstate is deposited as the activator. The activator, cesium tungstate, gives an unexpected increase in activity and selectivity as compared with potassium tungstate, which is used exclusively at the present state of the art.
01 Aug 1997-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the kinetics of the reduction of pure iron oxide and iron tungstate were investigated by thermogravimetric method in the temperature ranges of 1023 to 1173 K and 823 to 1100 K, respectively.
Abstract: The kinetics of the reduction of FeO and FeWO4 have been investigated by thermogravimetric method in the temperature ranges of 1023 to 1173 K and 823 to 1173 K, respectively The experiments were conducted under isothermal conditions in flowing hydrogen gas The activation energies for the reduction of the pure iron oxide and iron tungstate were found to be 427 kJ/mol and 851 kJ/mol, respectively The results obtained show that the reduction of iron tungstate proceeds in one single step from FeWO4 to Fe3W2 and W The experimental data are compared with the information available in the literature, and the correlations between the results obtained in pure oxide systems and complex systems are discussed
TL;DR: In this article, the amorphous Zr tungstate can be used as a gel-generator for the production of the 188======Re medical radioisotope.
Abstract: ZrW 2
O
7
(OH,Cl)
2
·2H
2
O
has been synthesised by refluxing, followed by hydrothermal
crystallisation of amorphous zirconium tungstate gels in 1–8 m HCl.
It is known that the amorphous Zr tungstate can be used as a gel-generator
for production of the 188
Re medical radioisotope. The structure
of ZrW 2
O
7
(OH,Cl)
2
·2H
2
O
has been refined by conventional powder diffractometer data. The compound
crystallises in the tetragonal space group
I4
1
cd (no. 110) with a=11.4454(4),
c=12.4851(7) A, Z=8 and
D
c
=3.74 g cm
-3
. Rietveld refinement
has been carried out from X-ray diffraction data using
Co-Kα radiation over the angular range 15–105°
(2θ) and converged with R
wp
=8.85%,
R
p
=6.60%. The structure consists of regular
ZrO
7
pentagonal bipyramids and distorted WO
6
octahedra, connected in a three-dimensional framework. The terminal
hydroxy groups of tungsten polyhedra are statistically substituted by
Cl.
TL;DR: By using multinuclear magnetic resonance spectroscopy, D-gulonic acid is found to form ten and seven complexes, respectively, with tungsten(VI) and molybdenum(VI), in aqueous solution, depending on pH and metal-ligand molar ratios.
Patent•
29 Apr 1997TL;DR: In this article, a method for forming a solid state humidity sensor is disclosed, which comprises the steps of dissolving a tungstate salt into an aqueous solution, adjusting the pH of the aqueus salt solution to below 8.5, and forming one or a pair of electrodes on an insulating substrate.
Abstract: A method for forming a solid state humidity sensor is disclosed which comprises the steps of: (a) dissolving a tungstate salt into an aqueous solution; (b) adjusting the pH of the aqueous tungstate salt solution to below 8.5; (c) forming one or a pair of electrodes on an insulating substrate; (d) placing the substrate into the pH-adjusted aqueous tungstate salt solution and heating the aqueous solution containing the substrate at temperatures above 70° C. to thereby form a pyrochlore-type crystalline tungsten trioxide film over the electrode or pair of electrodes; and (e) forming another electrode over the pyrochlore-type crystalline tungsten trioxide film if only one electrode is formed during step (c). Alternatively, the pyrochlore-type crystalline tungsten trioxide film can be formed over or between the electrodes by heating the pH-adjusted aqueous tungstate salt solution to cause a precipitation of pyrochlore-type crystalline tungsten trioxide, then screen-printing the pyrochlore-type crystalline tungsten trioxide powder on one or both of the electrodes to thereby form a humidity sensing element. The pyrochlore-type crystalline tungsten trioxide is represented by the general formula of (M2 O)x WO3.zH2 O, in which M is a cation, x is about 0.5, and z, which is the amount of crystalline water contained in the crystal, is typically less than 2.
TL;DR: In this article, absorbent carbons, pore filled with molybdate and tungstate ions, are shown to be very effective catalysts for the oxidation of sulfides with 30% aqueous H{sub 2}O{sub2}.
TL;DR: In this article, an impregnation of MgO with aqueous ammonium paratungstate solutions has been shown to produce amorphous Mg tungstates for low (723 K) calcination temperatures, but crystalline compounds are formed after calcination above 973 K.
TL;DR: The reaction of tungstate with the γ-decatungstosilicate anion leads to [Si2W23O77(OH)]9− This anion results from the association of γ]-SiW10O36]8- and γ-[SiW11O39]8]- by a (μ-oxo)ditungstic group.
Abstract: The reaction of tungstate with the γ-decatungstosilicate anion leads to [Si2W23O77(OH)]9-. This anion results from the association of γ-[SiW10O36]8- and γ-[SiW11O39]8- by a (μ-oxo)ditungstic group.
Patent•
10 Jul 1997
TL;DR: In this paper, a moulded aluminium oxide catalyst containing an alkali tungstate s promoter is used for synthesis of methyl mercaptan, in an amount > 15 to 40 wt.% with respect to the total amount of catalyst.
Abstract: In a moulded aluminium oxide catalyst containing an alkali tungstate s promoter, used for synthesis of methyl mercaptan, the promoter is caesium tungstate (I) in an amount > 15 to 40 wt.% with respect to the total amount of catalyst.
TL;DR: In this paper, the photoluminescent properties of Eu3+ and SO42− doped zinc and magnesium polycrystalline tungstate systems are investigated, and two luminescent bands are characterized simultaneously the matrix emission spectrum.
TL;DR: In this paper, a new cathodic oxidation system for the oxidation of sulfoxides was developed, which involves the cathodic reduction of dioxygen to hydrogen peroxide which oxidizes tungstate to pertungstate in the solution, and sulfoxide are oxidized to the corresponding sulfones with the resulting tung state/pertungstate redox mediator.
Abstract: A new cathodic oxidation system for the oxidation of sulfoxides was developed. The system involves the cathodic reduction of dioxygen to hydrogen peroxide which oxidizes tungstate to pertungstate in the solution, and sulfoxides are oxidized to the corresponding sulfones with the resulting tungstate/ pertungstate redox mediator in high effiency and selectivity.
TL;DR: In this article, a zirconia aerogel was doped with both tungstate and sulfate by sequential incipient wetness impregnations, and the role of the dopants and activation temperature on the physical and chemical properties was studied.
Abstract: A zirconia aerogel, prepared by a sol-gel route followed by supercritical drying, was doped with both tungstate and sulfate by sequential incipient wetness impregnations. The role of the dopants and activation temperature on the physical and chemical properties was studied. The materials were characterized by nitrogen adsorption, X-ray diffraction, n-butane isomerization, Raman and infrared spectroscopy. Tungstate and sulfate were catalytically active over non-overlapping ranges of activation temperature and thus offered no synergistic catalytic effects. The effects of the two dopants on each other appeared to be primarily physical.
TL;DR: In this paper, mixed NiMo-W oxides have been prepared by decomposition at======873 K of Anderson-type [NiMo====== 6-x====== W oxides] (x=0, 2, 3, 4, 6) heteropolyoxometallates.
Abstract: Mixed Ni–Mo–W oxides have been prepared by decomposition at
873 K of Anderson-type [NiMo
6-x
W
x
O
24
H
6
](NH
4
)
4
5H
2
O (x=0, 2, 3, 4, 6) heteropolyoxometallates.
Thermal analysis of the precursors, X-ray diffraction and Raman
spectroscopy on the mixed oxides were performed. X-Ray powder patterns,
collected at the end of the thermal treatment, revealed that the final
products are NiMoO
4
and MoO
3
for the x=0
composition, whereas for tungsten-containing materials the final products
are Mo
1-x
W
x
O
3
solid solutions, NiWO
4
and WO
3
, depending on the
Mo/W atomic ratio. Raman spectra have confirmed the XRPD analysis,
revealing the presence of a stable WO
3
-type phase at high
molybdenum contents and a high structural stability of
Mo
1-x
W
x
O
3
solid
solutions.
Patent•
06 May 1997
TL;DR: In this article, the tungsten (VI) compound is a salt containing a cationic apart and an anionic part selected from a group composed of a tungstate and an isopolytungstate.
Abstract: PROBLEM TO BE SOLVED: To obtain a medical composition having low toxicity and useful as an insulin placebo used for curing of diabetes mellitus without inducing serious adverse effect, containing tungsten (VI) compounds. SOLUTION: This composition contains a tungsten (VI) compound and its solvate or addition salt, e.g. sodium tungstate dihydrate as an active component. A tungsten (VI) compound is innocent in an effective using amount for both of a short period and a long period without inducing hypoglycemia even in excessively administrating and can be used as an oral medicine for treating of type 1 diabetes an type 2 diabetes. The tungsten (VI) compound is a salt containing a cationic apart and an anionic part selected from a group composed of a tungstate and an isopolytungstate. An administrating amount of this composition is 0.5-500mg/kg/day, preferably 50-500mg/kg/day.
TL;DR: In this article, the pyrochlore tungstate thin film has been prepared by an autoclave hydrothermal method at a temperature of 200 °C. The film was characterized by X-ray diffractometry, Xray photoelectron spectroscopy and scanning electron micrograph measurements.
TL;DR: In this paper, the starting materials for crystal growth Tungsten trioxide (WO 3 ) and zinc oxide (ZnO) were prepared by homogenous precipitation (using hydrogen peroxide as a complexing agent for sodium tungstate) and liquid liquid extraction techniques, respectively.
TL;DR: Fourier transform infrared spectra of tetraamminecopper(II) molybdate and tungstate and their partially deuterated analogues were recorded at room temperature (RT) and at boiling temperature of liquid nitrogen (LNT).